354 results on '"Wolter, H. H."'
Search Results
2. Medium effects on freeze-out of light clusters at NICA energies
- Author
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Roepke, G., Blaschke, D., Ivanov, Yu. B., Karpenko, Iu., Rogachevsky, O. V., and Wolter, H. H.
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Nuclear Theory ,High Energy Physics - Phenomenology - Abstract
We estimate the chemical freeze-out of light nuclear clusters for NICA energies of above 2 A GeV. On the one hand we use results from the low energy domain of about 35 A MeV, where medium effects have been shown to be important to explain experimental results. On the high energy side of LHC energies the statistical model without medium effects has provided results for the chemical freeze-out. The two approaches extrapolated to NICA energies show a discrepancy that can be attributed to medium effects and that for the deuteron/proton ratio amounts to a factor of about three. These findings underline the importance of a detailed investigation of light cluster production at NICA energies., Comment: 10 pages, 4 figures, accepted for publication in Phys. Part. Nucl. Lett; typo in Eq. (6) corrected in v2 more...
- Published
- 2017
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Catalog
3. Elliptic Flow and the Nuclear Equation of State
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Trautmann, W. and Wolter, H. H.
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Nuclear Experiment ,Nuclear Theory - Abstract
New constraints for the nuclear equation of state at suprasaturation densities have been obtained by measuring collective particle flows in heavy-ion reactions at relativistic energies. Ratios and differences of neutron and hydrogen flows in 197Au + 197Au collisions at 400 MeV/nucleon were used in studies of the asymmetric-matter equation of state. The comparison with predictions of transport models favors a moderately soft to linear density dependence, consistent with ab-initio nuclear matter theories. Model predictions suggest that comprehensive data sets collected at higher bombarding energies will provide information on the asymmetric-matter equation of state in the density range up to two or three times the saturation value., Comment: 20 pages, 9 figures, paper dedicated to the memory of Prof. Walter Greiner, to appear in Walter Greiner Memorial Volume (World Scientific). arXiv admin note: substantial text overlap with arXiv:1205.2585 more...
- Published
- 2017
4. Results of the ASY-EOS experiment at GSI: The symmetry energy at suprasaturation density
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Russotto, P., Gannon, S., Kupny, S., Lasko, P., Acosta, L., Adamczyk, M., Al-Ajlan, A., Al-Garawi, M., Al-Homaidhi, S., Amorini, F., Auditore, L., Aumann, T., Ayyad, Y., Basrak, Z., Benlliure, J., Boisjoli, M., Boretzky, K., Brzychczyk, J., Budzanowski, A., Caesar, C., Cardella, G., Cammarata, P., Chajecki, Z., Chartier, M., Chbihi, A., Colonna, M., Cozma, M. D., Czech, B., De Filippo, E., Di Toro, M., Famiano, M., Gašparić, I., Grassi, L., Guazzoni, C., Guazzoni, P., Heil, M., Heilborn, L., Introzzi, R., Isobe, T., Kezzar, K., Kiš, M., Krasznahorkay, A., Kurz, N., La Guidara, E., Lanzalone, G., Fèvre, A. Le, Leifels, Y., Lemmon, R. C., Li, Q. F., Lombardo, I., Lukasik, J., Lynch, W. G., Marini, P., Matthews, Z., May, L., Minniti, T., Mostazo, M., Pagano, A., Pagano, E. V., Papa, M., Pawlowski, P., Pirrone, S., Politi, G., Porto, F., Reviol, W., Riccio, F., Rizzo, F., Rosato, E., Rossi, D., Santoro, S., Sarantites, D. G., Simon, H., Skwirczynska, I., Sosin, Z., Stuhl, L., Trautmann, W., Trifirò, A., Trimarchi, M., Tsang, M. B., Verde, G., Veselsky, M., Vigilante, M., Wang, Yongjia, Wieloch, A., Wigg, P., Winkelbauer, J., Wolter, H. H., Wu, P., Yennello, S., Zambon, P., Zetta, L., and Zoric, M. more...
- Subjects
Nuclear Experiment - Abstract
Directed and elliptic flows of neutrons and light charged particles were measured for the reaction 197Au+197Au at 400 MeV/nucleon incident energy within the ASY-EOS experimental campaign at the GSI laboratory. The detection system consisted of the Large Area Neutron Detector LAND, combined with parts of the CHIMERA multidetector, of the ALADIN Time-of-flight Wall, and of the Washington-University Microball detector. The latter three arrays were used for the event characterization and reaction-plane reconstruction. In addition, an array of triple telescopes, KRATTA, was used for complementary measurements of the isotopic composition and flows of light charged particles. From the comparison of the elliptic flow ratio of neutrons with respect to charged particles with UrQMD predictions, a value \gamma = 0.72 \pm 0.19 is obtained for the power-law coefficient describing the density dependence of the potential part in the parametrization of the symmetry energy. It represents a new and more stringent constraint for the regime of supra-saturation density and confirms, with a considerably smaller uncertainty, the moderately soft to linear density dependence deduced from the earlier FOPI-LAND data. The densities probed are shown to reach beyond twice saturation., Comment: 25 pages, 22 figures, accepted for publication in Physical Review C more...
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- 2016
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5. Light cluster production at NICA
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Bastian, N. -U., Batyuk, P., Blaschke, D., Danielewicz, P., Ivanov, Yu. B., Karpenko, Iu., Röpke, G., Rogachevsky, O., and Wolter, H. H.
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Nuclear Theory ,Nuclear Experiment - Abstract
Light cluster production at the NICA accelerator complex offers unique possibilities to use these states as "rare probes" of in-medium characteristics such as phase space occupation and early flow. In order to explain this statement, in this contribution theoretical considerations from the nuclear statistical equilibrium model and from a quantum statistical model of cluster production are supplemented with a discussion of a transport model for light cluster formation and with results from hydrodynamic simulations combined with the coalescence model., Comment: 7 pages, 7 figures, accepted for publication in Eur. Phys. J. A more...
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- 2016
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6. Siegert State Approach to Quantum Defect Theory
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Hategan, C., Ionescu, R. A., and Wolter, H. H.
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Physics - Atomic Physics ,Nuclear Theory - Abstract
The Siegert states are approached in framework of Bloch-Lane-Robson formalism for quantum collisions. The Siegert state is not described by a pole of Wigner R- matrix but rather by the equation $1- R_{nn}L_n = 0$, relating R- matrix element $R_{nn}$ to decay channel logarithmic derivative $L_n$. Extension of Siegert state equation to multichannel system results into replacement of channel R- matrix element $R_{nn}$ by its reduced counterpart ${\cal R}_{nn}$. One proves the Siegert state is a pole, $(1 - {\cal R}_{nn} L_{n})^{-1}$, of multichannel collision matrix. The Siegert equation $1 - {\cal R}_{nn} L_{n} = 0$, ($n$ - Rydberg channel), implies basic results of Quantum Defect Theory as Seaton's theorem, complex quantum defect, channel resonances and threshold continuity of averaged multichannel collision matrix elements. more...
- Published
- 2016
7. A way forward in the study of the symmetry energy: experiment, theory, and observation
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Horowitz, C. J., Brown, E. F., Kim, Y., Lynch, W. G., Michaels, R., Ono, A., Piekarewicz, J., Tsang, M. B., and Wolter, H. H.
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Nuclear Theory ,Astrophysics - High Energy Astrophysical Phenomena ,Nuclear Experiment - Abstract
The symmetry energy describes how the energy of nuclear matter rises as one goes away from equal numbers of neutrons and protons. This is very important to describe neutron rich matter in astrophysics. This article reviews our knowledge of the symmetry energy from theoretical calculations, nuclear structure measurements, heavy ion collisions, and astronomical observations. We then present a roadmap to make progress in areas of relevance to the symmetry energy that promotes collaboration between the astrophysics and the nuclear physics communities., Comment: 19 pages, results from first International Collaborations in Nuclear Theory (ICNT) program at NSCL/FRIB, submitted to J. Phys G more...
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- 2014
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8. Effects of the liquid-gas phase transition and cluster formation on the symmetry energy
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Typel, S., Wolter, H. H., Röpke, G., and Blaschke, D.
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Nuclear Theory ,Nuclear Experiment - Abstract
Various definitions of the symmetry energy are introduced for nuclei, dilute nuclear matter below saturation density and stellar matter, which is found in compact stars or core-collapse supernovae. The resulting differences are exemplified by calculations in a theoretical approach based on a generalized relativistic density functional for dense matter. It contains nucleonic clusters as explicit degrees of freedom with medium dependent properties that are derived for light clusters from a quantum statistical approach. With such a model the dissolution of clusters at high densities can be described. The effects of the liquid-gas phase transition in nuclear matter and of cluster formation in stellar matter on the density dependence of the symmetry energy are studied for different temperatures. It is observed that correlations and the formation of inhomogeneous matter at low densities and temperatures causes an increase of the symmetry energy as compared to calculations assuming a uniform uncorrelated spatial distribution of constituent baryons and leptons., Comment: 20 pages, 19 figures, version accepted for publication in EPJA special volume on Nuclear Symmetry Energy more...
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- 2013
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9. The ASY-EOS experiment at GSI: investigating the symmetry energy at supra-saturation densities
- Author
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Russotto, P., Chartier, M., De Filippo, E., Févre, A. Le, Gannon, S., Gašparić, I., Kiš, M., Kupny, S., Leifels, Y., Lemmon, R. C., Łukasik, J., Marini, P., Pagano, A., Pawłowski, P., Santoro, S., Trautmann, W., Veselsky, M., Acosta, L., Adamczyk, M., Al-Ajlan, A., Al-Garawi, M., Al-Homaidhi, S., Amorini, F., Auditore, L., Aumann, T., Ayyad, Y., Baran, V., Basrak, Z., Benlliure, J., Boiano, C., Boisjoli, M., Boretzky, K., Brzychczyk, J., Budzanowski, A., Cardella, G., Cammarata, P., Chajecki, Z., Chbihi, A., Colonna, M., Cozma, D., Czech, B., Di Toro, M., Famiano, M., Geraci, E., Greco, V., Grassi, L., Guazzoni, C., Guazzoni, P., Heil, M., Heilborn, L., Introzzi, R., Isobe, T., Kezzar, K., Krasznahorkay, A., Kurz, N., La Guidara, E., Lanzalone, G., Lasko, P., Li, Q., Lombardo, I., Lynch, W. G., Matthews, Z., May, L., Minniti, T., Mostazo, M., Papa, M., Pirrone, S., Politi, G., Porto, F., Reifarth, R., Reisdorf, W., Riccio, F., Rizzo, F., Rosato, E., Rossi, D., Simon, H., Skwirczynska, I., Sosin, Z., Stuhl, L., Trifiró, A., Trimarchi, M., Tsang, M. B., Verde, G., Vigilante, M., Wieloch, A., Wigg, P., Wolter, H. H., Wu, P., Yennello, S., Zambon, P., Zetta, L., and Zoric, M. more...
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Nuclear Experiment - Abstract
The elliptic-flow ratio of neutrons with respect to protons in reactions of neutron rich heavy-ions systems at intermediate energies has been proposed as an observable sensitive to the strength of the symmetry term in the nuclear Equation Of State (EOS) at supra-saturation densities. The recent results obtained from the existing FOPI/LAND data for $^{197}$Au+$^{197}$Au collisions at 400 MeV/nucleon in comparison with the UrQMD model allowed a first estimate of the symmetry term of the EOS but suffer from a considerable statistical uncertainty. In order to obtain an improved data set for Au+Au collisions and to extend the study to other systems, a new experiment was carried out at the GSI laboratory by the ASY-EOS collaboration in May 2011., Comment: Talk given by P. Russotto at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS) more...
- Published
- 2012
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10. Cluster virial expansion for nuclear matter within a quasiparticle statistical approach
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Ropke, G., Bastian, N. -U., Blaschke, D., Klahn, T., Typel, S., and Wolter, H. H.
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Nuclear Theory ,High Energy Physics - Phenomenology - Abstract
Correlations in interacting many-particle systems can lead to the formation of clusters, in particular bound states and resonances. Systematic quantum statistical approaches allow to combine the nuclear statistical equilibrium description (law of mass action) with mean-field concepts. A chemical picture, which treats the clusters as distinct entities, serves as an intuitive concept to treat the low-density limit. Within a generalized Beth-Uhlenbeck approach, the quasiparticle virial expansion is extended to include arbitrary clusters, where special attention must be paid to avoid inconsistencies such as double counting. Correlations are suppressed with increasing density due to Pauli blocking. The contribution of the continuum to the virial coefficients can be reduced by considering clusters explicitly and introducing quasiparticle energies. The cluster-virial expansion for nuclear matter joins known benchmarks at low densities with those near saturation density., Comment: 18 pages, 6 figures, 2 tables more...
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- 2012
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11. Elliptic flow and the symmetry energy at supra-saturation density
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Trautmann, W. and Wolter, H. H.
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Nuclear Experiment ,Nuclear Theory - Abstract
The elliptic flow in collisions of neutron-rich heavy-ion systems at intermediate energies emerges as an observable sensitive to the strength of the symmetry energy at supra-saturation densities. First results obtained by comparing ratios or differences of neutron and hydrogen flows with predictions of transport models favor a moderately soft to linear density dependence, consistent with ab-initio nuclear-matter theories. Comprehensive data sets of high accuracy can be expected to improve our knowledge of the equation of state of asymmetric nuclear matter., Comment: 16 pages, 8 figures, to appear as a review article in International Journal of Modern Physics E more...
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- 2012
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12. Symmetry energy of dilute warm nuclear matter
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Natowitz, J. B., Ropke, G., Typel, S., Blaschke, D., Bonasera, A., Hagel, K., Klahn, T., Kowalski, S., Qin, L., Shlomo, S., Wada, R., and Wolter, H. H.
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Nuclear Theory - Abstract
The symmetry energy of nuclear matter is a fundamental ingredient in the investigation of exotic nuclei, heavy-ion collisions and astrophysical phenomena. New data from heavy-ion collisions can be used to extract the free symmetry energy and the internal symmetry energy at subsaturation densities and temperatures below 10 MeV. Conventional theoretical calculations of the symmetry energy based on mean-field approaches fail to give the correct low-temperature, low-density limit that is governed by correlations, in particular by the appearance of bound states. A recently developed quantum statistical (QS) approach that takes the formation of clusters into account predicts symmetry energies that are in very good agreement with the experimental data. A consistent description of the symmetry energy is given that joins the correct low-density limit with quasiparticle approaches valid near the saturation density., Comment: 4 pages, 2 figures, 1 table more...
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- 2010
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13. Probing the symmetry energy at high baryon density with heavy ion collisions
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Greco, V., Colonna, M., Di Toro, M., and Wolter, H. H.
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Nuclear Theory ,Nuclear Experiment - Abstract
The nuclear symmetry energy at densities above saturation density ($\rho_0\sim 0.16 fm^{-3}$) is poorly constrained theoretically and very few relevant experimental data exist. Its study is possible through Heavy Ion Collisions (HIC) at energies $E/A> 200$ MeV, particularly with beams of neutron-rich radioactive nuclei. The energy range implies that the momentum dependence of the isospin fields, i.e. the difference of the effective masses on protons and neutrons, also has to be investigated before a safe constraint on $\esy(\rho)$ is possible. We discuss the several observables which have been suggested, like $n/p$ emission and their collective flows and the ratio of meson yields with different isospin projection, $\pi^-/\pi^+$ and $K^0/K^+$. We point out several physical mechanisms that should be included in the theoretical models to allow a direct comparison to the more precise experiments which will be able to distinguish the isospin projection of the detected particles: CSR/Lanzhou, FAIR/GSI, RIBF/RIKEN, FRIB/MSU., Comment: 12 opages, 5 figures, Proceedings of IWND09 - 22-25 August 2009 Shanghai (China) more...
- Published
- 2009
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14. Composition and thermodynamics of nuclear matter with light clusters
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Typel, S., Röpke, G., Klähn, T., Blaschke, D., and Wolter, H. H.
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Nuclear Theory ,Astrophysics - Solar and Stellar Astrophysics ,Nuclear Experiment - Abstract
We investigate nuclear matter at finite temperature and density, including the formation of light clusters up to the alpha particle The novel feature of this work is to include the formation of clusters as well as their dissolution due to medium effects in a systematic way using two many-body theories: a microscopic quantum statistical (QS) approach and a generalized relativistic mean field (RMF) model. Nucleons and clusters are modified by medium effects. Both approaches reproduce the limiting cases of nuclear statistical equilibrium (NSE) at low densities and cluster-free nuclear matter at high densities. The treatment of the cluster dissociation is based on the Mott effect due to Pauli blocking, implemented in slightly different ways in the QS and the generalized RMF approaches. We compare the numerical results of these models for cluster abundances and thermodynamics in the region of medium excitation energies with temperatures T <= 20 MeV and baryon number densities from zero to a few times saturation density. The effect of cluster formation on the liquid-gas phase transition and on the density dependence of the symmetry energy is studied. Comparison is made with other theoretical approaches, in particular those, which are commonly used in astrophysical calculations. The results are relevant for heavy-ion collisions and astrophysical applications., Comment: 32 pages, 15 figures, minor corrections, accepted for publication in Physical Review C more...
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- 2009
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15. Isospin Effects on Strangeness in Heavy-Ion Collisions
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Prassa, V., Gaitanos, T., Ferini, G., Di Toro, M., Lalazissis, G. A., and Wolter, H. H.
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Nuclear Theory - Abstract
Kaon properties are studied within the framework of a fully covariant transport approach. The kaon-nucleon potential is evaluated in two schemes, a chiral perturbative approach and an effective One-Boson-Exchange model. Isospin effects are explicitly accounted for in both models. The transport calculations indicate a significant sensitivity of momentum distributions and total yields of $K^{0,+}$ isospin states on the choice of the kaon-nucleon interaction. Furthermore, isospin effects are rather moderate on absolute kaon yields, but appear on strangeness ratios. This is an important issue in determining the high density symmetry energy from studies of strangeness production in heavy-ion collisions., Comment: 15 papes, 5 figures. Accepted for publication in Nuclear Physics more...
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- 2009
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16. The High-Density Symmetry Energy in Heavy Ion Collisions
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Wolter, H. H., Prassa, V., Lalazissis, G. A., Gaitanos, T., Ferini, G., Greco, V., and Di Toro, M.
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Nuclear Theory - Abstract
The nuclear symmetry energy as a function of density is rather poorly constrained theoretically and experimentally both below saturation density, but particularly at high density, where very few relevant experimental data exist. We discuss observables which could yield information on this question, in particular, proton-neutron flow differences, and the production of pions and kaons in relativistic heavy ion collisions. For the meson production we investigate particularly ratios of the corresponding isospin partners $\pi^-/\pi^+$ and $K^0/K^+$, where we find that the kaons are an interesting probe to the symmetry energy. In this case we also discuss the influnece of various choices for the kaon potentials or in-medium effective masses., Comment: 7 pages, 5 figures. Proceedings of the 2008 Erice School on Nuclear Physics more...
- Published
- 2008
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17. Isospin Dynamics in Heavy Ion Collisions: from Coulomb Barrier to Quark Gluon Plasma
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Di Toro, M., Baran, V., Colonna, M., Ferini, G., Gaitanos, T., Giordano, V., Greco, V., Bo, Liu, Zielinska-Pfabe, M., Plumari, S., Prassa, V., Rizzo, C., Rizzo, J., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium nuclear interaction in regions away from saturation. In this report we present a selection of new reaction observables in dissipative collisions particularly sensitive to the symmetry term of the nuclear Equation of State (Iso-EoS). We will first discuss the Isospin Equilibration Dynamics. At low energies this manifests via the recently observed Dynamical Dipole Radiation, due to a collective neutron-proton oscillation with the symmetry term acting as a restoring force. At higher beam energies Iso-EoS effects will be seen in Imbalance Ratio Measurements, in particular from the correlations with the total kinetic energy loss. For fragmentation reactions in central events we suggest to look at the coupling between isospin distillation and radial flow. In Neck Fragmentation reactions important $Iso-EoS$ information can be obtained from the correlation between isospin content and alignement. The high density symmetry term can be probed from isospin effects on heavy ion reactions at relativistic energies (few AGeV range). Rather isospin sensitive observables are proposed from nucleon/cluster emissions, collective flows and meson production. The possibility to shed light on the controversial neutron/proton effective mass splitting in asymmetric matter is also suggested. A large symmetry repulsion at high baryon density will also lead to an "earlier" hadron-deconfinement transition in n-rich matter. A suitable treatment of the isovector interaction in the partonic EoS appears very relevant., Comment: 18 pages, 12 figures, lecture at the 2008 Erice School on Nuclear Physics, to appear in Progress in Particle and Nuclear Physics more...
- Published
- 2008
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18. Asymmetry of velocity distributions in peripheral collisions at Fermi energies
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Mikhailova, T. I., Erdemchimeg, B., Kaminski, G., Artyukh, A. G., Colonna, M., Di Toro, M., Mikhailov, I. N., Sereda, Yu. M., and Wolter, H. H.
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Nuclear Theory - Abstract
Asymmetry of the velocity distributions of projectile like fragments produced in heavy-ion collisions is discussed. The calculations made in transport model approach (the solution of Vlasov kinetic equation with the collisions term) are compared with experimental data for the reactions $^{22}Ne$ ($40 A\cdot$MeV) + $^{9}$Be and $^{18}$O ($35 A\cdot$MeV) + $^9$Be ($^{181}$Ta) at forward angles. It is found that the velocity distributions appear to be composed of two contributions: a direct component centered at beam velocity and a dissipative component at lower energies, leading to an asymmetry of the velocity distributions. The direct component is interpreted empirically in the Goldhaber model, and the widths and centroids of the distributions are extracted. The remaining dissipative (also called deep-inelastic) contributions are then well described by the transport calculations. It is shown that the ratio of yields of direct and dissipative contributions, which determines the asymmetry of velocity distribution, depends on the shape of the deflection function., Comment: 13 pages, 5 figures, talk delivered at the International Meeting on Nuclear Spectroscopy and Nuclear Structure (Nucleus 2008), Moscow (Russia), June 23--27, 2008 more...
- Published
- 2008
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19. Competition of breakup and dissipative processes in peripheral collisions at Fermi energies
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Mikhailova, T. I., Artyukh, A. G., Colonna, M., Di Toro, M., Erdemchimeg, B., Kaminski, G., Mikhailov, I. N., Sereda, Yu. M., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
Heavy ion collisions in the Fermi energy regime may simultaneously show features of direct and dissipative processes. To investigate this behavior in detail, we study isotope and velocity distributions of projectile-like fragments in the reactions $^{18}$O (35 $A\cdot$MeV) + $^9$Be($^{181}$Ta) at forward angles. We decompose the experimental velocity distributions empirically into two contributions: a direct, `breakup' component centered at beam velocity and a dissipative component at lower velocities leading to a tail of the velocity distributions. The direct component is interpreted in the Goldhaber model, and the widths of the velocity distributions are extracted. The dissipative component is then successfully described by transport calculations. The ratio of the yields of the direct and the dissipative contributions can be understood from the behavior of the deflection functions. The isotope distributions of the dissipative component agree qualitatively with the data, but the modification due to secondary de-excitation needs to be considered. We conclude, that such reactions are of interest to study the equilibration mechanism in heavy ion collisions., Comment: 8 pages, 5 figures, talk delivered at the International Conference on Current Problems in Nuclear Physics and Atomic Energy (NPAE-Kyiv'2008) more...
- Published
- 2008
20. Investigation of Low-Density Symmetry Energy via Nucleon and Fragment Observables
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Wolter, H. H., Rizzo, J., Colonna, M., Di Toro, M., Greco, V., Baran, V., and Zielinska-Pfabe, M.
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Nuclear Theory - Abstract
With stochastic transport simulations we study in detail central and peripheral collisions at Fermi energies and suggest new observables, sensitive to the symmetry energy below normal density. As such we identify on one hand the isospin imbalance ratio, i.e. the relative amount of isospin equilibration in binary, peripheral reactions of nuclei with different isospin, as a function of the energy loss, which is sensitive to isospin diffusion; on the other hand the isospin asymmetry of an intermediate mass fragment (IMF) in symmetric collisions in ternary reactions, or more particularly, the ratio of the IMF to the residue asymmetry, which is sensitive to isospin migration., Comment: 6 pages, 6 figures; Contrib. to Int. Symp. on Exotic States of Nuclear Matter (EXOCT2007), Catania, Italy, June 2007, World Scientifc style more...
- Published
- 2007
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21. Isospin Effects on Meson Production in Relativistic Heavy Ion Collisions
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Di Toro, M., Colonna, M., Ferini, G., Greco, V., Rizzo, J., Baran, V., Gaitanos, T., Bo, Liu, Lalazissis, G., Prassa, V., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We show that the phenomenology of isospin effects on heavy ion reactions at intermediate energies (few AGeV range) is extremely rich and can allow a ``direct'' study of the covariant structure of the isovector interaction in a high density hadron medium. We work within a relativistic transport frame, beyond a cascade picture, consistently derived from effective Lagrangians, where isospin effects are accounted for in the mean field and collision terms. We show that rather sensitive observables are provided by the pion/kaon production (\pi^-/\pi^+, K^0/K^+ yields). Relevant non-equilibrium effects are stressed. The possibility of the transition to a mixed hadron-quark phase, at high baryon and isospin density, is finally suggested. Some signatures could come from an expected ``neutron trapping'' effect., Comment: 8 pages, 3 figures; HADRON07, XII Int.Conf. on Hadron Spectroscopy, Frascati Oct. 2007. Latex frascatiphys.sty more...
- Published
- 2007
22. Isospin Dynamics in Peripheral Heavy Ion Collisions at Fermi Energies
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Rizzo, J., Colonna, M., Baran, V., Di Toro, M., Wolter, H. H., and Zielinska-Pfabe, M.
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Nuclear Theory - Abstract
We present a detailed study of isospin dynamics in peripheral collisions at Fermi energies. We consider symmetric and mixed collisions of (124,112)Sn isotopes at 35 and 50 AMeV to study the isospin transport between the different reaction components (residues, gas and possibly intermediate mass fragments) and, in particular, the charge equilibration in the mixed system. We evaluate the effects of drift terms due to asymmetry and density gradients, which are directly related to the poorly known value and slope of the symmetry energy below saturation density. We verify the importance of an isoscalar momentum dependence of the mean field, which is found to influence the isospin transport since it changes the reaction times. We finally suggest two observables particularly sensitive to the isovector part of the nuclear equation-of-state: the correlation between isospin equilibration and kinetic energy loss for binary events, and the isospin content of the produced mid-rapidity fragments for neck fragmentation events., Comment: 34 pages, 15 figures, Nucl.Phys. A, in press more...
- Published
- 2007
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23. Constraining the Symmetry Energy: A Journey in the Isospin Physics from Coulomb Barrier to Deconfinement
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Di Toro, M., Colonna, M., Greco, V., Ferini, G., Rizzo, C., Rizzo, J., Baran, V., Gaitanos, T., Prassa, V., Wolter, H. H., and Zielinska-Pfabe, M.
- Subjects
Nuclear Theory - Abstract
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium nuclear interaction in regions away from saturation. In this work we present a selection of reaction observables in dissipative collisions particularly sensitive to the isovector part of the interaction, i.e. to the symmetry term of the nuclear Equation of State (EoS). At low energies the behavior of the symmetry energy around saturation influences dissipation and fragment production mechanisms. We will first discuss the recently observed Dynamical Dipole Radiation, due to a collective neutron-proton oscillation during the charge equilibration in fusion and deep-inelastic collisions. Important Iso-EOS effects are stressed. Reactions induced by unstable 132Sn beams appear to be very promising tools to test the sub-saturation Isovector EoS. New Isospin sensitive observables are also presented for deep-inelastic, fragmentation collisions and Isospin equilibration measurements (Imbalance Ratios). The high density symmetry term can be derived from isospin effects on heavy ion reactions at relativistic energies (few AGeV range), that can even allow a ``direct'' study of the covariant structure of the isovector interaction in the hadron medium. Rather sensitive observables are proposed from collective flows and from pion/kaon production. The possibility of the transition to a mixed hadron-quark phase, at high baryon and isospin density, is finally suggested. Some signatures could come from an expected ``neutron trapping'' effect. The importance of studying violent collisions with radioactive beams from low to relativistic energies is finally stressed., Comment: 15 pages, 5 figures, Int.Workshop on Nuclear Dynamics in Heavy Ion Reactions and Neutron Stars, Beijing Normal Univ. July 07, to appear in Int.Journ.Modern Physics E (2008) more...
- Published
- 2007
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24. Isospin Distillation with Radial Flow: a Test of the Nuclear Symmetry Energy
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Colonna, M., Baran, V., Di Toro, M., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We discuss mechanisms related to isospin transport in central collisions between neutron-rich systems at Fermi energies. A fully consistent study of the isospin distillation and expansion dynamics in two-component systems is presented in the framework of a stochastic transport theory. We analyze correlations between fragment observables, focusing on the study of the average N/Z of fragments, as a function of their kinetic energy. We identify an EOS-dependent relation between these observables, allowing to better characterize the fragmentation path and to access new information on the low density behavior of the symmetry energy., Comment: 4 pages, 4 figures (revtex4) more...
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- 2007
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25. In-medium effects on particle production in heavy ion collisions
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Prassa, V., Ferini, G., Gaitanos, T., Wolter, H. H., Lalazissis, G. A., and Di Toro, M.
- Subjects
Nuclear Theory - Abstract
The effect of possible in-medium modifications of nucleon-nucleon ($NN$) cross sections on particle production is investigated in heavy ion collisions ($HIC$) at intermediate energies. In particular, using a fully covariant relativistic transport approach, we see that the density dependence of the {\it inelastic} cross sections appreciably affects the pion and kaon yields and their rapidity distributions. However, the $(\pi^{-}/\pi^{+})$- and $(K^{0}/K^{+})$-ratios depend only moderately on the in-medium behavior of the inelastic cross sections. This is particularly true for kaon yield ratios, since kaons are more uniformly produced in high density regions. Kaon potentials are also suitably evaluated in two schemes, a chiral perturbative approach and an effective meson-quark coupling method, with consistent results showing a similar repulsive contribution for $K^{+}$ and $K^{0}$. As a consequence we expect rather reduced effects on the yield ratios. We conclude that particle ratios appear to be robust observables for probing the nuclear equation of state ($EoS$) at high baryon density and, particularly, its isovector sector., Comment: 29 pages, 15 figures, accepted for publication in Nuclear Physics A more...
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- 2007
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26. Proton Threshold States in the 22Na(p,gamma)23Mg Reaction and Astrophysical Implications
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Comisel, H., Hategan, C., Graw, G., and Wolter, H. H.
- Subjects
Nuclear Theory ,Astrophysics - Abstract
Proton threshold states in 23Mg are important for the astrophysically relevant proton capture reaction 22Na(p,gamma)23Mg. In the indirect determination of the resonance strength of the lowest states, which were not accessible by direct methods, some of the spin-parity assignments remained experimentally uncertain. We have investigated these states with Shell Model, Coulomb displacement, and Thomas-Ehrman shift calculations. From the comparison of calculated and observed properties we relate the lowest relevant resonance state at E=7643 keV to an excited 3/2+ state in accordance with a recent experimental determination by Jenkins et al.. From this we deduce significantly improved values for the 22Na(p,gamma)23Mg reaction rate at stellar temperatures below T_9=0.1K., Comment: 8 pages, 4 figures, 6 tables more...
- Published
- 2006
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27. Isospin Dynamics in Heavy Ion Collisions: EoS-sensitive Observables
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Di Toro, M., Baran, V., Colonna, M., Ferini, G., Gaitanos, T., Greco, V., Rizzo, J., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium nuclear interaction in regions away from saturation and at high nucleon momenta. In this report we present a selection of reaction observables particularly sensitive to the isovector part of the interaction, i.e. to the symmetry term of the nuclear Equation of State (EoS) At low energies the behavior of the symmetry energy around saturation influences dissipation and fragment production mechanisms. Predictions are shown for deep-inelastic and fragmentation collisions induced by neutron rich projectiles. Differential flow measurements will also shed lights on the controversial neutron/proton effective mass splitting in asymmetric matter. The high density symmetry term can be derived from isospin effects on heavy ion reactions at relativistic energies (few AGeV range), that can even allow a ``direct'' study of the covariant structure of the isovector interaction in the hadron medium. Rather sensitive observables are proposed from collective flows and from pion/kaon production. The possibility of the transition to a mixed hadron-quark phase, at high baryon and isospin density, is finally suggested. Some signatures could come from an expected ``neutron trapping'' effect., Comment: 10 pages, 5 figures; espcrc1 style; IX Int.Conf. on Nucleus-Nucleus Collisions, Rio de Janeiro Aug.2006; to appear in Nucl.Phys.A more...
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- 2006
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28. Heavy Ion Collisions at Relativistic Energies: Testing a Nuclear Matter at High Baryon and Isospin Density
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Di Toro, M., Colonna, M., Ferini, G., Gaitanos, T., Greco, V., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We show that the phenomenology of isospin effects on heavy ion reactions at intermediate energies (few AGeV range) is extremely rich and can allow a ``direct'' study of the covariant structure of the isovector interaction in the hadron medium. We work within a relativistic transport frame, beyond a cascade picture, consistently derived from effective Lagrangians, where isospin effects are accounted for in the mean field and collision terms. Rather sensitive observables are proposed from collective flows (``differential'' flows) and from pion/kaon production ($\pi^-/\pi^+$, $K^0/K^+$ yields). For the latter point relevant non-equilibrium effects are stressed. The possibility of the transition to a mixed hadron-quark phase, at high baryon and isospin density, is finally suggested. Some signatures could come from an expected ``neutron trapping'' effect., Comment: 8 pages, 4 figures, espcrc1 (latex) style. Conf. "Perspectives in Hadronic Physics", ICTP Trieste May 2006, Nucl.Phys. A, to appear more...
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- 2006
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29. Isospin effects on sub-threshold kaon production at intermediate energies
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Ferini, G., Gaitanos, T., Colonna, M., Di Toro, M., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We show that in collisions with neutron rich heavy ions at energies around the production threshold K^0 and K^+ yields might probe the isospin dependent part of the nuclearEquation of State (EoS) at high baryon densities. In particular we suggest the K^0/K^+ ratio as a promising observable. Results obtained in a fully covariant relativistic transport approach are presented for central Au+Au collisions in the beam energy range 0.8-1.8~AGeV. The focus is put on the EoS influence which goes beyond the "collision-cascade" picture. The isovector part of the in-medium interaction affects the kaon multiplicities via two mechanisms: i) a "symmetry potential" effect, i.e. a larger neutron repulsion in n-rich systems (isospin fractionation); ii) a "threshold" effect, due to the change in the self-energies of the particles involved in inelastic processes. Genuine relativistic contributions are revealed, that could allow to directly ``measure'' the Lorentz structure of the effective isovector interaction., Comment: 5 pages, 2 figures, revtex4 more...
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- 2006
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30. Constraints on the high-density nuclear equation of state from the phenomenology of compact stars and heavy-ion collisions
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Klahn, T., Blaschke, D., Typel, S., van Dalen, E. N. E., Faessler, A., Fuchs, C., Gaitanos, T., Grigorian, H., Ho, A., Kolomeitsev, E. E., Miller, M. C., Ropke, G., Trumper, J., Voskresensky, D. N., Weber, F., and Wolter, H. H. more...
- Subjects
Nuclear Theory ,Astrophysics ,High Energy Physics - Phenomenology - Abstract
A new scheme for testing nuclear matter equations of state (EsoS) at high densities using constraints from neutron star phenomenology and a flow data analysis of heavy-ion collisions is suggested. An acceptable EoS shall not allow the direct Urca process to occur in neutron stars with masses below $1.5~M_{\odot}$, and also shall not contradict flow and kaon production data of heavy-ion collisions. Compact star constraints include the mass measurements of 2.1 +/- 0.2 M_sun (1 sigma level) for PSR J0751+1807, of 2.0 +/- 0.1 M_sun from the innermost stable circular orbit for 4U 1636-536, the baryon mass - gravitational mass relationships from Pulsar B in J0737-3039 and the mass-radius relationships from quasiperiodic brightness oscillations in 4U 0614+09 and from the thermal emission of RX J1856-3754. This scheme is applied to a set of relativistic EsoS constrained otherwise from nuclear matter saturation properties with the result that no EoS can satisfy all constraints simultaneously, but those with density-dependent masses and coupling constants appear most promising., Comment: 15 pages, 8 figures, 5 tables more...
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- 2006
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31. Modelization of the EOS
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Fuchs, C. and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
This article summarizes theoretical predictions for the density and isospin dependence of the nuclear mean field and the corresponding nuclear equation of state. We compare predictions from microscopic and phenomenological approaches. An application to heavy ion reactions requires to incorporate these forces into the framework of dynamical transport models. Constraints on the nuclear equation of state derived from finite nuclei and from heavy ion reactions are discussed., Comment: 17 pages, 13 figures, contributed paper to the World Consensus Initiative (WCI) book "Dynamics and Thermodynamics with Nucleonic Degrees of Freedom" more...
- Published
- 2005
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32. Effects of In-Medium NN Cross Sections on Particle Production
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Prassa, V., Gaitanos, T., Wolter, H. H., Lalazissis, G., and Di Toro, M.
- Subjects
Nuclear Theory - Abstract
The in-medium modification of nucleon-nucleon (NN) cross sections is investigated by means of particle production in heavy ion collisions (HIC) at intermediate energies. In particular, the density dependence of the {\it inelastic} cross sections considerably affects the pion and kaon yields and their rapidity distributions. However, the $(\pi^{-}/\pi^{+})$- and $(K^{+}/K^{0})$-ratios depend only moderately on the in-medium behavior of the inelastic cross sections. It turns out that particle ratios seem to be robust observables in determining the nuclear equation of state (EoS) and, particularly, its isovector sector., Comment: 6 pages, 4 figures more...
- Published
- 2005
33. Isospin Transport at Fermi Energies
- Author
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Baran, V., Colonna, M., Di Toro, M., Zielinska-Pfabe, M., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
In this paper we investigate isospin transport mechanisms in semi-peripheral collisions at Fermi energies. The effects of the formation of a low density region (neck) between the two reaction partners and of pre-equilibrium emission on the dynamics of isospin equilibration are carefully analyzed. We clearly identify two main contributions to the isospin transport: isospin diffusion due to the $N/Z$ ratio and isospin drift due to the density gradients. Both effects are sensitive to the symmetry part of the nuclear Equation of State (EOS), in particular to the value and slope around saturation density., Comment: 6 pages, 6 figures, revtex4-twocolumns more...
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- 2005
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34. Nuclear stopping and flow in heavy ion collisions and the in-medium NN cross section
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Gaitanos, T., Fuchs, C., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We present transport calculations for heavy ion reactions in which the mean field and the in-medium nucleon-nucleon cross section are consistently based on the same effective interaction, i.e. the in-medium T-matrix from microscopic Dirac-Brueckner calculations. Doing so, the stopping in central reactions in terms of the recently proposed $var_{\rm tl}$ observable and the correlation to the behavior of the directed flow is investigated. The relation to the nuclear shear viscosity is discussed., Comment: 9 pages, 4 figures more...
- Published
- 2004
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35. Asymmetric Colliding Nuclear Matter Approach in Heavy Ion Collisions
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Gaitanos, T., Fuchs, C., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
The early stage of a heavy ion collision is governed by local non-equilibrium momentum distributions which have been approximated by colliding nuclear matter configurations, i.e. by two Lorentz elongated Fermi ellipsoids. This approach has been extended from the previous assumption of symmetric systems to asymmetric 2-Fermi sphere configurations, i.e. to different densities. This provides a smoother transition from the limiting situation of two interpenetrating currents to an equilibrated system. The model is applied to the dynamical situations of heavy ion collisions at intermediate energies within the framework of relativistic transport (RBUU) calculations. We find that the extended colliding nuclear matter approach is more appropriate to describe collective reaction dynamics in terms of flow observables, in particular, for the elliptic flow at low energies., Comment: 21 pages, 8 figures, accepted for publication in Nuclear Physics A more...
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- 2004
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36. Fragmentation path of excited nuclear systems
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Colonna, M., Fabbri, G., Di Toro, M., Matera, F., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We perform a study of the fragmentation path of excited nuclear sources, within the framework of a stochastic mean-field approach. We consider the reaction $^{129}$Xe + $^{119}$Sn at two beam energies: 32 and 50 MeV/A, for central collisions. It is observed that, after the compression phase the system expands towards a dilute configuration from which it may recontract or evolve into a bubble-like structure. Then fragments are formed through the development of volume and/or surface instabilities. The two possibilities co-exist at 32 MeV/A, leading to quite different fragment partitions, while at 50 MeV/A the hollow configuration is observed in all events. Large variances are recovered in a way fully consistent with the presence of spinodal decomposition remnants. Kinematical properties of fragments are discussed and suggested as observables very sensitive to the dominant fragment production mechanism. A larger radial collective flow is observed at 50 MeV/A, in agreement with experiments., Comment: 13 pages, 7 figures, submitted to Nucl.Phys.A more...
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- 2004
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37. Stopping and Isospin Equilibration in Heavy Ion Collisions
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Gaitanos, T., Colonna, M., Di Toro, M., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We investigate the density behaviour of the symmetry energy with respect to isospin equilibration in the combined systems $Ru(Zr)+Zr(Ru)$ at relativistic energies of 0.4 and $1.528 AGeV$. The study is performed within a relativistic framework and the contribution of the iso-vector, scalar $\delta$ field to the symmetry energy and the isospin dynamics is particularly explored. We find that the isospin mixing depends on the symmetry energy and a stiff behaviour leads to more transparency. The results are also nicely sensitive to the "fine structure" of the symmetry energy, i.e. to the covariant properties of the isovector meson fields. The isospin tracing appears much less dependent on the in-medium neutron-proton cross-sections ($\sigma_{np}$) and this makes such observable very peculiar for the study of the isovector part of the nuclear equation of state. Within such a framework, comparisons with experiments support the introduction of the $\delta$ meson in the description of the iso-vector equation of state., Comment: 11 pages, 5 figures. Accepted for publication in Phys.Lett.B more...
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- 2004
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38. Isospin effects in intermediate energy heavy ion collisions
- Author
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Gaitanos, T., Di Toro, M., Ferini, G., Colonna, M., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We investigate the density dependence of the symmetry energy in a relativistic description by decomposing the iso-vector mean field into contributions with different Lorentz properties. We find important effects of the iso-vector, scalar $\delta$ channel on the density behavior of the symmetry energy. Finite nuclei studies show only moderate effects originating from the virtual $\delta$ meson. In heavy ion collisions from Fermi to relativistic energies up to $1-2 AGeV$ one finds important contributions on the dynamics arising from the different treatment of the microscopic Lorentz structure of the symmetry energy. We discuss a variety of possible signals which could set constraints on the still unknown density dependence of the symmetry energy, when experimental data will be available. Examples of such observables are isospin collective flow, threshold production of pions and kaons, isospin equilibration and stopping in asymmetric systems like $Au+Au$, $Sn+Sn$ and $Ru(Zr)+Zr(Ru)$., Comment: 9 pages, 5 figures, proceedings of the XLII International Winter Meeting On Nuclear Physics, Bormio (Italy) January 256-February 1, 2004 more...
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- 2004
39. On the Lorentz structure of the symmetry energy
- Author
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Gaitanos, T., Di Toro, M., Typel, S., Baran, V., Fuchs, C., Greco, V., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We investigate in detail the density dependence of the symmetry energy in a relativistic description by decomposing the iso-vector mean field into contributions with different Lorentz covariant properties. We find important effects of the iso-vector, scalar channel (i.e. $\delta$-meson like) on the high density behavior of the symmetry energy. Applications to static properties of finite nuclei and to dynamic situations of heavy ion collisions are explored and related to each other. The nuclear structure studies show only moderate effects originating from the virtual $\delta$ meson. At variance, in heavy ion collisions one finds important contributions on the reaction dynamics arising from the different Lorentz structure of the high density symmetry energy when a scalar iso-vector $\delta$ field is introduced. Particularly interesting is the related neutron/proton effective mass splitting for nucleon transport effects and for resonance and particle production around the threshold. We show that the $\delta$-like channel turns out to be essential for the production of pions, when comparing with experimental data, in particular for high momentum selections., Comment: 30 pages, 12 figures (.eps) more...
- Published
- 2003
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40. Relativistic effects in the search for high density symmetry energy
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Greco, V., Baran, V., Colonna, M., Di Toro, M., Gaitanos, T., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
Intermediate energy heavy ion collisions open the unique possibility to explore the Equation of State ($EOS$) of nuclear matter far from saturation, in particular the density dependence of the symmetry energy. Within a relativistic transport model it is shown that the isovector-scalar $\delta$-meson, which affects the high density behavior of the symmetry energy density, influences the dynamics of heavy ion collisions in terms of isospin collective flows. The effect is largely enhanced by a relativistic mechanism related to the covariant nature of the fields contributing to the isovector channel. Results for reactions induced by $^{132}Sn$ radioactive beams are presented. The elliptic flows of nucleons and light isobars appear to be quite sensitive to microscopic structure of the symmetry term, in particular for particles with large transverse momenta, since they represent an earlier emission from a compressed source. Thus future, more exclusive, experiments with relativistic radioactive beams should be able to set stringent constraints on the density dependence of the symmetry energy far from ground state nuclear matter., Comment: 11 pages, 4 figures inserted in the text. Elsevier preprint format (Latex) Version with a new figure for the more physical 132Sn+124Sn case more...
- Published
- 2002
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41. Non-Equilibrium and Collective Flow Effects in Relativistic Heavy Ion Collisions
- Author
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Gaitanos, T., Wolter, H. H., and Fuchs, C.
- Subjects
Nuclear Theory - Abstract
We discuss the problems involved in extracting the nuclear equation-of-state from heavy-ion collisions. We demonstrate that the equation of state becomes effectively softer in non-equilibrium and this effect is observable in terms of collective flow effects. Thus, non-equilibrium effects must be included in transport descriptions on the level of the effective mean fields. A comparison with transverse momentum, rapidity, and centrality selected flow data show the reliability and limitations of the underlying interaction which was derived from microscopic Dirac-Brueckner (DB) results., Comment: 11 pages, 6 figures, to be published in the proceedings of the 3rd International Balkan School on Nuclear Physics, Thessaloniki, Greece, 18-24.09.2002 more...
- Published
- 2002
42. Relativistic Mean Field Model with Generalized Derivative Nucleon-Meson Couplings
- Author
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Typel, S., Chossy, T. v., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
The quantum hadrodynamics (QHD) model with minimal nucleon-meson couplings is generalized by introducing couplings of mesons to derivatives of the nucleon field in the Lagrangian density. This approach allows an effective description of a state-dependent in-medium interaction in the mean-field approximation. Various parametrizations for the generalized couplings are developed and applied to infinite nuclear matter. In this approach, scalar and vector self-energies depend on both density and momentum similarly as in the Dirac-Brueckner theory. The Schr\"{o}diger-equivalent optical potential is much less repulsive at high nucleon energies as compared to standard relativistic mean field models and thus agrees better with experimental findings. The derivative couplings in the extended model have significant effects on properties of symmetric nuclear matter and neutron matter., Comment: 35 pages, 1 table, 10 figures more...
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- 2002
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43. Isotope yields from central 112,124Sn+112,124Sn collisions, dynamical emission?
- Author
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Liu, T. X., Liu, X. D., van Goethem, M. J., Lynch, W. G., Shomin, R., Tan, W. P., Tsang, M. B., Verde, G., Wagner, A., Xi, H. F., Xu, H. S., Colonna, M., Di Toro, M., Zielinska-Pfabe, M., Wolter, H. H., Beaulieu, L., Davin, B., Larochelle, Y., Lefort, T., de Souza, R. T., Yanez, R., Viola, V. E., Charity, R. J., and Sobotka, L. G. more...
- Subjects
Nuclear Experiment - Abstract
Isotopic yields for light particles and intermediate mass fragments have been measured for 112Sn+112Sn, 112Sn+124Sn, 124Sn+112Sn and 124Sn+124Sn central collisions at E/A=50 MeV and compared with predictions of stochastic mean field calculations. These calculations predict a sensitivity of the isotopic distributions to the density dependence of the asymmetry term of the nuclear equation of state. However, the secondary decay of the excited fragments modifies significantly the primary isotopic distributions and these modifications are rather sensitive to theoretical uncertainties in the excitation energies of the hot fragments. The predicted final isotope distributions are narrower than the experimental data and the sensitivity of the predicted yields to the density dependence of the asymmetry term is reduced., Comment: 30 pages, 7 figures more...
- Published
- 2002
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44. Isospin effects in Nuclear Fragmentation
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Baran, V., Colonna, M., Di Toro, M., Greco, V., Zielinska-Phabe, M., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We investigate properties of the symmetry term in the equation-of-state (EOS) of nuclear matter (NM) from the analysis of simulations of fragmentation events in intermediate energy heavy ion collisions. For charge asymmetric systems a qualitative new feature in the liquid-gas phase transition is predicted: the onset of chemical instabilities with a mixture of isoscalar and isovector components. This leads to a separation into a higher density (``liquid'') symmetric and a low density (``gas'') neutron-rich phase, the so-called neutron distillation effect. We analyse the simulations with respect to the time evolution of the isospin dynamics, as well as with respect to the distribution and asymmetry of the final primary fragments. Qualitatively different effects arise in central collisions, with bulk fragmentation, and peripheral collisions with neck-fragmentation. The neck fragments produced in this type of process appear systematically more neutron-rich from a dynamical nucleon migration effect which is very sensitive to the symmetry term in regions just below normal density. In general the isospin dynamics plays an important role in all the steps of the reaction, from prompt nucleon emission to the sequential decay of the primary fragments. A fully microscopic description of the reaction dynamics including stochastic elements to treat fluctuations realistically is absolutely necessary in order to extract precise information on the fragmentation and the nuclear equation of state. We have performed simulations for fragment production events in $n$-rich ($^{124}Sn$) and $n$-poor ($^{112}Sn$) symmetric colliding systems., Comment: 31 pages, 18 Postscript figures, minor changes more...
- Published
- 2001
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45. Testing Dirac-Brueckner models in collective flow of heavy-ion collisions
- Author
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Gaitanos, T., Fuchs, C., Wolter, H. H., and Faessler, Amand
- Subjects
Nuclear Theory - Abstract
We investigate differential in-plane and out-of-plane flow observables in heavy ion reactions at intermediate energies from $0.2\div 2$ AGeV within the framework of relativistic BUU transport calculations. The mean field is based on microscopic Dirac-Brueckner-Hartree-Fock (DBHF) calculations. We apply two different sets of DBHF predictions, those of ter Haar and Malfliet and more recent ones from the T\"ubingen group, which are similar in general but differ in details. The latter DBHF calculations exclude spurious contributions from the negative energy sector to the mean field which results in a slightly softer equation of state and a less repulsive momentum dependence of the nucleon-nucleus potential at high densities and high momenta. For the application to heavy ion collisions in both cases non-equilibrium features of the phase space are taken into account on the level of the effective interaction. The systematic comparison to experimental data favours the less repulsive and softer model. Relative to non-relativistic approaches one obtains larger values of the effective nucleon mass. This produces a sufficient amount of repulsion to describe the differential flow data reasonably well., Comment: 14 pages Revtex, 19 figures, discussion extended and two figures added, accepted for publication in EPJA more...
- Published
- 2001
46. Asymmetry Effects on Nuclear Fragmentation
- Author
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Di Toro, M., Baran, V., Colonna, M., Maccarone, S., Zielinska-Pfabe, M., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We show the possibility of extracting important information on the symmetry term of the Equation of State ($EOS$) directly from multifragmentation reactions using stable isotopes with different charge asymmetries. We study n-rich and n-poor $Sn + Sn$ collisions at $50AMeV$ using a new stochastic transport approach with all isospin effects suitably accounted for. For central collisions a chemical component in the spinodal instabilities is clearly seen. This effect is reduced in the neck fragmentation observed for semiperipheral collisions, pointing to a different nature of the instability. In spite of the low asymmetry tested with stable isotopes the results are showing an interesting and promising dependence on the stiffness of the symmetry term, with an indication towards an increase of the repulsion above normal density., Comment: 8 pages (Latex), 7 Postscript figures, CRIS2000 Conference, Acicastello, Italy, May 22-26, (2000), Nucl. Phys. A (in press) more...
- Published
- 2000
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47. What can we learn from Nuclear Matter Instabilities?
- Author
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Baran, V., Colonna, M., Di Toro, M., Zielinska-Pfabe, M., and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
We discuss the features of instabilities in binary systems, in particular, for asymmetric nuclear matter. We show its relevance for the interpretation of results obtained in experiments and in "ab initio" simulations of the reaction between $^{124}Sn+^{124}Sn$ at 50AMeV.}, Comment: 6 pages, 4 Postscript figures, talk at Bologna 2000 - Stucture of the Nucleus at the Dawn of the Century, May 29 -Jun 3, Bologna, Italy, 2000 more...
- Published
- 2000
- Full Text
- View/download PDF
48. Thermodynamical description of heavy ion collisions
- Author
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Gaitanos, T., Wolter, H. H., and Fuchs, C.
- Subjects
Nuclear Theory - Abstract
We analyze the thermodynamical state of nuclear matter in transport descriptions of heavy ion reactions. We determine thermodynamical variables from an analysis of local momentum space distributions and compare to blast model parameters from an analysis of fragment energy spectra. These descriptions are applied to spectator and fireball matter in semi-central and central Au+Au collisions at SIS-energies, respectively., Comment: 4 pages, 2 postscript-figures, to be published in the proceedings of Bologna2000: Structure of the Nucleus at the Dawn of the Century, Bologna, Italy, 29 May - 3 Jun 2000 more...
- Published
- 2000
- Full Text
- View/download PDF
49. Can we determine the nuclear equation of state from heavy ion collisions?
- Author
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Gaitanos, T., Wolter, H. H., Fuchs, C., and Faessler, A.
- Subjects
Nuclear Theory - Abstract
We discuss the problems involved in extracting the nuclear equation-of-state from heavy-ion collisions. We demonstrate that the equation of state becomes effectively softer in non-equilibrium and this effect is observable in terms of collective flow effects. Thus, non-equilibrium effects must be included in transport descriptions on the level of the effective mean fields. A comparison with transverse momentum, rapidity, and centrality selected flow data show the reliability and limitations of the underlying interaction which was derived from microscopic Dirac-Brueckner (DB) results., Comment: 6 pages, 3 postscript-figures, to be published in the proceedings of Bologna2000: Structure of the Nucleus at the Dawn of the Century, Bologna, Italy, 29 May - 3 Jun 2000 more...
- Published
- 2000
- Full Text
- View/download PDF
50. Equal-time hierarchies for transport descriptions of fermionic fields
- Author
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Ionescu, R. A. and Wolter, H. H.
- Subjects
Nuclear Theory - Abstract
A transport theory which is not restricted to the gradient and quasi-particle approximations is presented which is formulated in terms of the energy moments, or equivalently the equal-time derivatives of the one-particle Green functions. A set of infinite hierarchies of kinetic and constraint equations for equal-time quantities for the spectral and the kinetic part of the one-particle Green function are derived. The hierarchies for the spectral function truncate automatically as in the mean field approximation. The possibility of a systematic truncation of the hierarchies for the kinetic part is discussed. The effects the quantum corrections are illustrated in a simple one-dimensional model., Comment: 34 pages, 4 figures more...
- Published
- 2000
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